1. Field of the Invention
The present invention relates to heat exchange technology and, in particular, relates to an improved seal that may be used to reduce leakage between a hot gas conduit and a cold air conduit of a regenerative heat exchanging system.
2. Description of the Related Art
Conventional regenerative heat exchangers are used with many types of machinery that exhaust hot gas and operate more efficiently when supplied with preheated air. These types of machinery include power plants, chemical processors, refineries, pulp and paper mills, and ship engines. Typically, two fluid stream passages extend through a heat exchanger. The first passage is an exhaust or hot gas conduit that communicates with a hot exhaust outlet of the machinery. Hot exhaust gases flow from the machinery exhaust into the hot gas conduit to the heat exchanger. The second passage is an intake or cold air conduit that communicates with a cold air intake passage of the machinery. The cold air conduit feeds air into the intake passage of the machinery. As is generally known in the art, the regenerative heat exchanger extracts heat from the exhaust gases of the machinery and transfers the heat to the cool air conduit, so that the machinery is supplied with heated intake air which improves the operating efficiency of the machinery.
A conventional heat exchanger typically includes a movable heat exchanging body that moves between the hot gas conduit and the cool air conduit. In most cases, the movable heat exchanging body cyclically collects heat from the exhaust conduit and transfers this heat energy to the intake conduit. One example of this type of heat exchanger may be referred to as a Ljungstrom™-style preheater. The heat exchanging body in a Ljungstrom-style preheater is typically cylindrical in shape and is located in a sealed relationship with an outer housing. The heat exchanging body, typically called a rotor, rotates about a center shaft within the housing of the heat exchanger. A plurality of radial walls extend radially outward from the center shaft and subdivide the heat exchanging body into a plurality of angular sectors. The angular sectors have a core material to provide a path for heated exhaust or intake air to travel through. The core is heated by the exhaust and the heat energy of the core is transferred to the intake air when the heated core is exposed to the intake air. As the heat exchanging body rotates, the angular sectors are alternatively exposed to the hot and cold conduits of the heat exchanging apparatus. Hence, as an angular sector of the heat exchanging body is exposed to the hot conduit, it absorbs heat from the exhaust gases of the machinery. The sector then rotatably moves and is exposed to the intake conduit where the sector then releases heat into the cool air that is passed into the machinery intake.
Unfortunately, a bypass gap exists between the rotor and the inner walls of the housing. Consequently, some heated gas in the exhaust conduit, may flow through the gap between the rotor and the inner wall of the housing and thereby bypass the core material in the rotor. To address this particular problem, seals are typically installed at the upper and lower surfaces of the rotor which extend into the gap between the outer surface of the rotor and the inner surface of the housing. These seals are referred to as either circumferential or bypass seals and they generally extend around the entire circumference of the rotor and occlude the opening between the inner wall of the housing and the outer wall of the rotor.
One difficulty associated with the use of these seals is that the rotor will generally deform during operation as a result of differential thermal expansion. This deformation is typically referred to as turndown and is often exhibited by the outer surfaces of the rotor sagging downward with respect to the center axis and toward the housing. Unfortunately, this may result in these seals becoming unduly worn or damaging the inner walls of the housing.
One possible solution is to use a seal that is flexible so that when the heat exchanger turns down, the seal can resiliently contact the sealing surface. A flexible seal can then be positioned substantially adjacent the sealing surface prior to turndown thereby allowing the seal to substantially occlude the bypass opening over the entire range of deformation of the rotor. However, as the seal will continuously be rubbing against the sealing surface, it is generally desirable that the seal be relatively thick so as to prolong the life of the seal against damage and the continuous wear of rubbing against the sealing surface. However, increasing the thickness of the seal to prolong the life of the seal against damage and wear naturally results in a decrease of the flexibility of the seal.
Certain prior art seals have been equipped with resilient interlocking features that provide independent flexibility while maintaining structural rigidity so as to elastically deform in response to contact with the sealing surface as a result of turndown of the heat exchanging body. For instance, U.S. Pat. No. 5,881,799 discloses an interlocking seal having structurally rigid resilient features that allow for flexible deformations. However, such seals may fracture or break when flexibly responding to rotational stress loads produced by rotation of the heat exchanging body with respect to the outer housing of the heat exchanger. As a result, stress fractures may allow gas leakage between conduits. In addition, the prior art seals typically comprise gaps between the interlocking features that may also allow for some heated gases in the hot gas conduit and some cold air in the cool air conduit to bypass the heat exchanging body. Therefore, while the prior art seals provide some improvement to efficiency loss in heat exchangers, they still result in inefficient operation as air and gases may bypass the heat exchanging body through bypass gaps between interlocking features.
Consequently, there currently exists a need for an improved seal that substantially reduces bypass gas leakage during rotation of the heat exchanging body. To this end, the improved seal should be structurally rigid, resilient, and flexible so that when the heat exchanging body deforms as a result of turndown, the improved seal maintains resilient contact with the sealing surface so as to withstand a significant amount of wear as a result of continuous rubbing contact with the sealing surface.